Recently, the membrane modules are used for filtration, separation, or the like of a liquid or a gas widely in the industrial field, the medical field, the food field, or the like. Particularly in the industrial field, a membrane module having a function of filtration of a solvent, separation of a gas in a liquid, pervaporation, or the like is requested.
As the membrane module used in these fields, conventionally, a membrane module using a flat membrane has been used commonly. However, recently, a membrane module using a hollow fiber membrane, which provides a membrane area per volume of the membrane module larger than that of the membrane module using the flat membrane, that is, a hollow fiber membrane module comprising a potting part produced by disposing a hollow fiber membrane in a module case and fixing the module case and the hollow fiber member with each other by bonding with a potting resin in a fluid-tight or airtight manner is used.
Since the filtration or the separation using the hollow fiber membrane module is carried out under the condition with a pressure applied from the primary side to the secondary side, the high sealing property and bonding property are required between the module case and the hollow fiber membrane so that a thermosetting resin such as an epoxy resin and a urethane resin has been used conventionally as the potting resin.
Here, at the time of potting the hollow fiber membrane module with a potting material, in order to realize the high sealing property as mentioned above, a method of disposing the hollow fiber membrane module in a centrifugal separator and applying a centrifugal force to the hollow fiber membrane module by rotating the same has been adopted commonly for facilitating impregnation of the potting resin to a bundle of the hollow fiber membranes.
In the case of potting the conventionally used thermosetting resin such as an epoxy resin and a urethane resin by the centrifugal method, as to the viscosity of the thermosetting resin at a room temperature, since a range without the risk of causing the impregnation failure in the hollow fiber membrane is selected, the impregnation failure cannot be caused basically, and thus the impregnation failure is caused extremely rarely. Therefore, a problem concerning the sealing property or the bonding property has not been generated to the hollow fiber membrane module to be obtained on the whole.
That is, according to the hollow fiber membrane module using the thermosetting resin, although the control of the temperature accuracy at a high level is preferable in terms of the quality control of the hollow fiber membrane module, since the tolerant temperature range in the centrifugal potting method is relatively wide, the need of the control is not high so that a centrifugal type production apparatus comprising a means therefor has not been proposed so far.
In the case the hollow fiber membrane module using a thermosetting resin as the potting resin is utilized for the pervaporation, the filtration of a solvent, the process of a solvent, or the like, depending on the solvent or the chemical, the potting resin is swelled and eluted so as to generate a crack, or the like, and accompanied therewith, a problem of deterioration of the bonding property, generation of leakage, purity deterioration of the processed matter, or the like can be generated.
In order to improve the shortcomings of the potting resin such as an epoxy resin and a urethane resin, a method of obtaining a hollow fiber membrane module by forming a potting part by using a thermoplastic resin such as a polyethylene resin as the potting resin, introducing a molten product of the potting resin among the hollow fiber membranes of a potting working part, and cooling and solidifying the same has been proposed.
For example, according to JP, A, 1-293105, a method having steps of stopping end part of the hollow fiber membrane by preliminarily filling calcium carbonate, or a mixture of calcium carbonate and calcined gypsum into the inside of the end part, filling a potting resin comprising a thermoplastic resin among the hollow fiber membranes, heating to a temperature of 50 to 150% of the melting point of the resin comprising the hollow fiber membrane, potting the outer circumference of the hollow fiber membrane bundle while fastening it with a thermally contracting tape, and eliminating the stopping material using a chemical, wherein a furnace capable of partially heating the hollow fiber membrane module is used as the means for heating the potting resin with the temperature range set at a temperature higher than the melting point of the resin comprising the hollow fiber membrane by 10 to 100° C., preferably by 20 to 50° C. has been proposed. According to the partial heating and the temperature setting, the hollow fiber membranes can be impregnated with the potting resin in a state placed still.
However, according to the production apparatus, the heating temperature range has the 90° C. temperature difference, with the 30° C. temperature difference tolerated in the preferable case, which is set in a still wide temperature range, and thus the degree of contraction or melting of the hollow fiber membranes in the temperature range is not constant.
Furthermore, according to the production apparatus, depending on the potting process in a state placed still, the impregnation of the hollow fiber membranes with the potting resin may not be preferable and the quality of the hollow fiber membrane module to be obtained is not constant.
Moreover, for example, JP, A, 8-266872 discloses a production method using thermoplastic resin powders as the potting resin, the production method comprising the steps of introducing a potting resin among hollow fiber membranes preliminarily separated, placing in a state placed still under a temperature of melting the potting resin using a heater block, taking the hollow fiber membrane bundle into a module case, and further applying a centrifugal force at the time of cooling the same to eliminate the voids generated at the time of cooling, solidification and contraction.
As to the heater block as the constituent member of the production apparatus used in this official gazette, there is no description concerning the control of the melting and heating temperature of the potting resin without paying any attention to the temperature control so that only the operation of melting the potting resin to be used is mentioned.
However, according to the production apparatus, without any special temperature control, the heater block temperature can usually be varied largely so that the viscosity of the molten potting resin can be fluctuated according to the temperature.
Therefore, the quality of the hollow fiber membrane module to be obtained such as the potting resin impregnation property and the bonding property cannot be stable. Moreover, according to the production apparatus, due to potting in a state placed still, the hollow fiber membranes may not be preferably impregnated with the potting resin so that the quality of the hollow fiber membrane module to be obtained is not constant.
Furthermore, according to the production apparatus used in the official gazette, as to the use of the centrifugal separator, only execution of the centrifugal cooling is mentioned without the intention of heating or temperature control thereof.
Therefore, according to the production apparatus disclosed in the official gazette, the viscosity of the potting resin was raised drastically by executing drawing and cooling at the same time without avoiding unimpregnation of the hollow fiber membranes of with the potting resin. As a result, the quality of the hollow fiber membrane module cannot be improved.
Moreover, for example, JP, A, 64-47409 discloses a hollow fiber membrane module with the end part of the hollow fiber membranes fixed with a potting resin having a melting point lower than the hollow fiber membrane. As to the operation of melting the potting resin and the operation of welding and fixing among the hollow fiber membranes, a heating operation is executed with various kinds of heaters, ovens, and ultrasonic welders in a combination with a desired pressuring operation or pressure reduction.
In contrast, the examples thereof disclose that welding and fixing may be executed while applying a vibration or a centrifugal force. As to a specific production apparatus, execution of a heating operation under a vacuum condition using an electric furnace, or furthermore, execution of filling among the hollow fiber membranes with a powdery potting resin using a vibrator at the time of heating are disclosed.
However, according to the electric furnace as the constituent member of the production apparatus, there is no disclosure about the control of the heating temperature. In general, in the case an electric furnace is used at a temperature, the temperature can be higher than the set temperature. Since the viscosity of the molten potting resin is fluctuated according to the temperature so that the quality of the hollow fiber membrane module to be obtained such as the potting resin impregnation property and the bonding property cannot be stable.
Moreover, according to the production apparatus, even in the case of a vacuum state, the impregnation of the hollow fiber membranes with the potting resin cannot be preferable due to the potting process in a state placed still so that the quality of the hollow fiber membrane module to be obtained is not constant.
Furthermore, according to the production apparatus used in the official gazette, also in the case the vibrator and the vacuum source are used in a combination, since the viscosity of the potting resin is not homogeneous, the hollow fiber membranes cannot be impregnated with the potting resin homogeneously. As a result, the quality of the hollow fiber membrane module cannot be stabilized.
Furthermore, according to JP, A, 4-63117 and JP, A, 8-318139, a production method of using a thermoplastic resin powder as the potting resin, impregnating a potting working part of a hollow fiber membrane bundle with a highly concentrated suspension liquid having the resin powder, and heating at a temperature of the melting point of the potting resin or higher and the melting point of the resin comprising the hollow fiber membranes or lower for gradually cooling and solidifying is disclosed.
As the specific production method thereof, a method of using an oven heated to 110 to 120° C., and impregnating the polypropylene hollow fiber membranes with a polyethylene potting resin in a state placed still is disclosed.
However, according to the production method, temperature stains are present between 110 to 120° C., which is an ordinary temperature control range of an oven so that the viscosity of the potting resin differs, and thus the impregnation failure of the potting resin can hardly be avoided in a state placed still.